This invention relates generally to radio frequency mixers, and particularly to such mixers using a field effect transistor (FET) for receiving a radio frequency signal of microwave band.
Various types of microwave mixers have hitherto been developed and actualized. These mixers can be divided into two categories, one being single-ended mixers utilizing a single mixing element, and the other being balanced mixers utilizing a plurality of mixing elements. Furthermore, the characteristic of a mixer drastically varies depending on the type of the mixing element, namely, diodes, transistors or FETs.
When a diode or diodes are used as the mixing element of a microwave mixer, although there is an advantage that a relatively wide band can be covered, such a mixer suffers from a drawback that conversion loss necessarily occurs when an input radio frequency signal is converted into an intermediate frequency signal.
Furthermore, some other mixers using a pluality of mixing diodes are apt to be complex in structure.
In mixers using FET(s), it is necessary that the power of a local oscillator signal is sufficiently large in order to reduce loss in input radio frequency signal.